Neutrino Mass and Mixing in the Seesaw Playground

TL;DR

This paper explores a simplified two right-handed neutrino model within the seesaw mechanism, aiming to predict neutrino mixing and CP violation by focusing on natural implementations that avoid large cancellations.

Contribution

It introduces a natural two right-handed neutrino framework, exemplified by the Littlest Seesaw, to enhance predictability of neutrino properties.

Findings

The model successfully predicts lepton mixing angles.

It provides specific predictions for CP violation phases.

The framework reduces parameter complexity in neutrino mass models.

Abstract

We discuss neutrino mass and mixing in the framework of the classic seesaw mechanism, involving right-handed neutrinos with large Majorana masses, which provides an appealing way to understand the smallness of neutrino masses. However, with many input parameters, the seesaw mechanism is in general not predictive. We focus on natural implementations of the seesaw mechanism, in which large cancellations do not occur, where one of the right handed neutrinos is dominantly responsible for the atmospheric neutrino mass, while a second right-handed neutrino accounts for the solar neutrino mass, leading to an effective two right-handed neutrino model. We discuss recent attempts to predict lepton mixing and CP violation within such natural frameworks, focussing on the Littlest Seesaw and its distinctive predictions.